Eight people, including seven children, were killed in a shooting at a school in the Russian city of Kazan on Tuesday.

The initial death toll was 11 people but that toll has since been lowered, the press office of the President of the Republic of Tatarstan, Rustam Minnikhanov, said.

The attack, which authorities say was allegedly carried out by a former student at the school, injured 21 people, including 18 children who were hospitalized. Six of them are in critical condition, according to the Tatarstan health ministry.

The 19-year-old perpetrator acted “alone”, the Tatarstan presidency spokesperson Lila Galímova said, denying Russian media reports of a second suspect.

The attacker, whose weapon was registered, has been arrested.

There were 714 children attending school and about 70 employees, including 52 teachers, when the shooting occurred.

Images posted on social media show pupils fleeing the school. Most of the students were evacuated to a neighboring kindergarten.

A criminal case has been opened to investigate the shooting.

Russian president Vladimir Putin has ordered a review of the regulation of permits for weapons possession in the wake of the shooting.